Prior to the present invention, bi-polar lead-acid and other electric charge storage batteries have been built with positive and negative electrode plates interleaved with one another and with glass mat separators all operatively mounted within an acid resistant battery case of polypropylene, or other suitable material which is heat sensitive to the prior terminal-electrode plate amalgamation processes. These prior batteries also have various fluid sealing structures and arrangements, and employ various methods of sealing that prevent or reduce the escape of electrolyte therefrom. While such batteries have been generally acceptable and have met requirements, new and improved constructions and methods are desired to meet higher standards for new and improved fluid sealed batteries with cases that are not damaged by the heat required for terminal strap-lug fusion. Accordingly, the present invention provides a higher standard for sealed batteries, and method of manufacture of such batteries.
In a preferred embodiment of this invention, a polypropylene case for a storage battery is molded with electric terminal units therein so that the terminal is completely surrounded by (e.g. embedded in) the material of the case so that there will be no significant leakage of the electrolyte from the case after the battery has been completely assembled.
The positive and negative terminal units of this invention feature elongated straps extending internal of the case and are slotted to from channels is therein to respectively receive the projecting lugs of corresponding internal positive and negative polarity lead based electrode plates, which are interleaved with one another and with glass mat separators. After the plates and separators are installed in the case, with the extending electrode plate lugs appropriately fitted in the channels of the straps.
The case is closed by a cover plate which is heat sealed thereto to form a substantially water tight assembly, but having amalgamation gas escape vent holes strategically located therein. The closed case is partially immersed in a tank containing a level of circulated cooling water supplied thereto without water leakage into the sealed case. With the polypropylene case being cooled by the circulated water to prevent heat damage thereto, a low voltage magnetic induction welding head assembly mounted within the tank can be energized to provide a high frequency welding field that heats the strap and the lugs of the electrode plates of one polarity in a burn zone so that the lugs and strap metals effectively fuse together.
Subsequently, the case is turned 180 degrees and the strap and lugs of the electrode plates of the opposite polarity are fused together in a second burn operation as described in connection with the first burn. The case is then removed from the tank and conveyed to a station where the electrolyte is added through the vent holes which are then sealed. One way valving is conventionally employed in the casing to allow a low pressure gas build up and release at the maximum allowed pressure. Most preferably flux and glass beads are inserted and packed in the void areas in the strap-lug amalgamation zone (i.e., in and about the lugs in the channel) before sealing the cover to the case. The burn zone is accordingly cleaned by the flux during burning while the lugs are laterally supported with respect to one another by the glass beads.
These and other features, advantages and objects of this invention will become more apparent from the following detailed description and drawings in which: